a) Field of the Invention
The invention relates to an improvement in optical near-field microscopes.
b) Description of Related Art
FIG. 1 shows the well-known construction of a SNOM arrangement. A near-field probe shaped as a tip SP is located at a distance of less than the light wavelength above the surface of a transparent specimen P. The specimen is held on a scanning table STI which is movable in the X/Y/z direction, so that the specimen can be scanned linewise by the tip SP. The scanning table STI is controlled by a control unit AE. The light which is not absorbed is collected by an objective O1 and its intensity is measured by a detector DT, for example, an avalanche diode or a PMT, arranged behind a pinhole PH for suppressing scattered light. An image of the surface of the specimen is composed from this. It is further known to reverse the light path and illuminate the specimen through the objective, the transmitted light being collected through the tip SP.
The scanning movement of the specimen results in restrictions in the specimen geometry and in the maximum attainable scanning speed. One reason against a scanning movement of the tip is that the probe and optical construction move relative to one another. Accordingly, it is not possible, for example, to detect the light emitted by the probe confocally or to illuminate confocally the specimen site under examination. The first arrangement is advantageous for suppression of scattered light, the second arrangement prevents bleaching out of dyes in fluorescence measurements. Moreover, it is not possible to stop down larger or smaller apertures (e.g., forbidden light).
It is the primary object of the invention to avoid these disadvantages. This object is met by a near-field optical microscope according to the invention, with a probe tip which is arranged on one side of a light transmitting specimen and moved in a scanning manner. The probe tip serves as a point light source, wherein optics for collecting light transmitted through the specimen and transmitting it to a detection unit or for collecting illumination light are provided on the other side of the specimen. The movement of the probe tip is adapted to on the detection side.